Since foreign substances contained in water form ice nuclei, water solidifies at 0° C. Such foreign substances are called ice nucleation active substances. Typical examples of known ice nucleation active substances include bacteria of the Pseudomonas genus, silver iodide, and the like. In contrast, pure water contains no foreign substances; therefore, ice nucleation does not occur. Even if pure water is cooled to a temperature lower than the freezing point (0° C.), for example, −39° C., pure water may not solidify (solidification). This is generally called “supercooling phenomenon.”
Some anti-ice nucleation activators (supercooling accelerators), which promote the supercooling phenomenon, have previously been reported. The anti-ice nucleation activators are capable of forming water that does not freeze even at a temperature under the freezing point. As a result, expansion upon freezing does not occur, which allows cells of plants or animals to be preserved without being destroyed. Even if it is frozen once, only fine ice nuclei are formed, resulting in the occurrence of fine ice crystal formation. Thus, the application of anti-ice nucleation activators to the fields of food, biomaterials (organ preservation), etc., is expected.
For example, low-molecular-weight compounds, such as eugenol, which is a component of a spice (see Non-Patent Literature (NPL) 1); as well as high-molecular-weight compounds, such as polysaccharide from Bacillus thuringiensis (see NPL 2), have been reported to exhibit anti-ice nucleation activity.
However, although these anti-ice nucleation activators exhibit anti-ice nucleation activity towards bacteria, such as Pseudomonas fluorescens, which is an ice nucleation active substance, they exhibit low anti-ice nucleation activity towards silver iodide. Moreover, due to safety issues, the use of the anti-ice nucleation activators was difficult in the fields of food, biomaterials, etc.